Microporous carbon ultrafine fibers with different diameter were prepared by electrospinning from resole-type phenolic resin, followed by heat curing and one-step carbonization, and their adsorption performance for benzene and water was evaluated. Average diameter of as-spun fibers changed from 1.1 to 0.33 mu m with increasing dimethylformamide content in the spinning solution, caused by more fiber divisions. The carbon ultrafine fibers with smaller diameter exhibited enhanced benzene adsorption and diminished water adsorption due to improved specific surface area, micropore volume and hydrophobicity. In addition, the relatively developed hydrophobicity of the prepared carbon ultrafine fibers resulted in much higher adsorption tendency for benzene over water, in comparison to common polyacrylonitrile-based electrospun activated carbon nanofibers. (C) 2013 Elsevier Ltd. All rights reserved.